Nacreous pigments currently used in coatings and plastics are predominantly coated micas. Nacreous pigments are made by forming a uniform coating of TiO2 on mica platelets; the mica serves as a transparent template so that the high refractive index TiO2 can assume the required platelet shape. Thicker platelets are produced to make interference colors. Light interference is created by interaction of the reflections from the upper and lower surfaces of the platelet, as well as interference between the reflected light and the light that passes through the platelets. A reflection maximum occurs at the wavelength of light for which the reflections from the upper and lower surfaces of the platelet are in phase. A reflection minimum occurs at the wavelength for such two reflections are exactly out of phase and cancel each other.
When nacreous pigments are incorporated into plastics and processed, they are subject to relatively high shear forces, for example, during extrusion. Under high shear conditions a portion of known nacreous pigments are stripped from the mica platelets, and the nacreous effect is muted.
Therefore, a need exists for a thermoplastic composition providing a nacreous effect on articles prepared from the thermoplastic composition and for which the nacreous effect is not negatively impacted upon exposure to high shear conditions.